Molybdenum recovery process



United States Patent 3,390,953 MOLYBDENUM RECOVERY PROCESS Albert E. Erhard, Denver, Colo., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed June 28, 1965, Ser. No. 467,714 8 Claims. (Cl. 23-16) ABSTRACT OF THE DISCLOSURE A process for the recovery of molybdenum from sources thereof containing alkaline earth molybdates by admixing a sulfate with the molybdenum source and contacting such admixture with HCl and an oxygen-containing gas at a temperature of at least 250 C. to volatilize the molybdenum therefrom as the chloride.

This invention relates to an improved process for the recovery of molybdenum from impu-re sources thereof wherein it occurs as an alkaline earth molybdate, and more particularly relates to an improved non-aqueous process for such recovery.

Present recovery of molybdenum from the various ores, sludges, slimes and concentrates in which it occurs is generally accomplished by aqueous or wet methods which involve digesting the ore in an aqueous acid or sintering with soda ash and subsequently recovering the molybdenum salt based on solubility in water. Likewise, it is known that some forms of molybdenum may be volatilized at elevated temperatures when contacted with HCl and air. However, when molybdenum occurs as an alkaline earth molybdate, such volatilization becomes highly inefficient and incomplete.

It is an object of this invention, therefore, to provide an improved process whereby the molybdenum values from such alkaline earth molybdates may be recovered in good yields by a non-aqueous process. The method for accomplishing this and other objects will be described in detail in the following specification.

It has now been discovered that molybdenum values may be recovered in high yields from molybdenum-containing sources wherein the molybdenum occurs as an alkaline earth molybdate by first adding to said molybdenum source a sulfate and contacting such-source with hydrochloric acid and an oxygen-containing gas at an elevated temperature to form and volatilize the molybdenum in a chloride form.

The process herein is applicable to virtually any source of molybdenum wherein it occurs as a molybdenum oxide or a molybdate but it finds particular application where such molybdenum occurs as an alkaline earth molybdate, i.e. a molybdate of magnesium, calcium, barium, strontium, or radium. In general, such process may be employed effectively on ores, sludges, slimes, concentrates or other impure molybdenum sources containing alkaline earth molybdates, particularly if the source contains calcium or magnesium molybdate.

For effective recovery of molybdenum values from such source, it is necessary to provide such molybdenum source with an amount of sulfate ion stoichiometrically equivalent to the alkaline earth molybdate contained therein. Such sulfate ion may be provided by sulfuric acid, by an ionizable salt of sulfuric acid such as sodium sulfate, potassium sulfate, lithium sulfate, ferric sulfate, and the like or by sulfur dioxide and air. In general, the sulfate is added to the ore or other molybdenum source and mixed well therewith prior to treatment with hydrochloric acid and air or other oxygen-containing source.

The sulfate-containing molybdenum source is heated to a temperature at least above the vaporization tempera- 300 C. to about 800 C. are desirable. Additional advantages are gained by treating the molybdenum source in the range of from about 400 C. to about 600 C. In this range, the reaction is more rapid than at lower temperatures and a minimum of side reaction occurs.

It is preferred to contact the heated sulfate-containing molybdenum source with a mixture of HCl and air in about equal volume proportions, but such proportions are not critical. The minimum quantity of either air and HCl should be that quantity necessary to react with the molybdenum present to form a volatile derivative. An amount of both air and HCl in excess of the amount theoretically required is generally preferred. Oxygen or any oxygencontaining gas may be used in the place of air but air is generally preferred because it is inexpensive and readily available.

The time of treatment of the sulfate-containing molybdenum source is not critical but, with good contact, a treatment time of from 10 minutes to several hours is generally employed depending on.the amount of Mo values present and upon the rate of HCl addition. Gas flow through the ore orother Mo source should, however, be sufliciently slow that the particles of ore or other material are not carried from the reaction zone by the gas stream.

It is necessary to the efficient operation of this process that good contact be made between the molybdenum source and the sulfate and betwen the sulfate-molybdenum mixture and the HCl and air. It is desirable, therefore, that the ore be in a form and size that will provide a relatively .high surface area. The sulfate then may be added to the granular or powdered molybdenum source as in a water solution or may, in the case of solid salts, be added as a granular or powered solid and intermixed therewith, or,;in the case of sulfur dioxide and air, be formed in the reaction zone and may be added together with the HCl gas. Contact with the HCl and air may then be accomplished in any suitable manner, e.g. the sulfatemolybdenum particles may be packed into a heated bed and the gaseous treating agents passed therethrough.

Treatment of an alkaline earth molybdate as described herein permits reaction of the combined molybdenum values with HCl and air to form a volatile molybdenum derivative, generally a chloride or oxychloride. Thi's volatile derivative passes into the vapor phase and is removed with the other-gases from the reaction zone. The relatively pure molybdenum in a chloride form may then be condensed on a cool surface and recovered or may be treated further while still in the vapor phase to produce other derivatives.

The following examples provide a detailed description of the operation of the invention but are not to be construed as limiting the scope of the invention thereto.

Example 1 As a blank, a mixture of 99 grams of a pure silica sand and 0.96 gram of MgMoO, was packed into a vertical high temperature glass tube which was placed in a furnace and heated to 600 C. A mixture containing equal volumes of air and HCl was then passed through the tube for 30 minutes at a rate such that a total of 3 grams of HCl was passed therethrough. Analysis of the residual sand showed 40.4 weight percent of the molybdenum had been removed therefrom. The volatilized molybdenum, as the oxychloride, collected on a cool portion ofthe tube."

In the same manner, a mixture of the same composition was treated at 600 C. with a gas mixture containing 65 vol. percent air, 30 vol.'percent"HCl and 5 vol. percent S for 30 minutes with a total of 2 grams of HCl. Analysis of the residual sand showed 99 percent of the molybdenum had been volatilized therefrom.

Example 2 In a similar manner, 99 grams of'silica sand, 0.96 gram of MgMoO and 1.5 grams of Na SO were mixed and placed in a vertical high temperature glass tube. The tube-was then placed in a furnace and heated to 600 C. A mixture of equal volumes of air and HCl was then passed therethrough for a period of 30 minutes at a rate such-that a total of 3 grams of HCl had passed therethrough. Analysis of the residual sand showed 94.4 Weight percent of the molybdenum had been removed therefrom. The volatilized molybdenum, as the oxychloride, collected on a cool portion of the tube.

Example 3 A 50 gram portion of a pure silica sand containing 1% Mo as CaMoO was packed into a vertical high temperature glass tube which was placed in a furnace and heated to 600 C. A gaseous mixture containing 30% by vol. of HCl and 70% by vol. air was then passed through the tube for 30 minutes at a rate such that a total of 2 grams of HCl was passed therethrough. Analysis of the residual sand showed that 72 weight percent of the molybdenum values had been voltalized therefrom. The volatilized molybdenum, as the oxychloride, collected on a cool portion of the tube.

A second 50 grams portion of the same CaMoO -containing mixture was treated in the same manner at 600 C.

for 30 minutes with a gaseous mixture containing 30% by vol. HCl, 65% by vol. air and 5% by vol. S0 The gas flow was such that a total of 2 grams of HCl was fed to the reaction zone. Analysis of the residual sand showed the 99.3 weight percent of the molybdenum had been volatilized. The volatilized molybdenum salt collected on a cool portion of the tube.

Example 4 grams of HCl and an equal volume of air passed therethrough in the manner of Example 1. Analysis of the ash after treatment showed 76% 0f the molybdenum had been removed therefrom.

I claim:

1. An improved. process for the recovery of molybdenum from sources thereof containing alkaline earth molybdates which comprises 1 t (l) contacting said molybdenum sourcewith a sulfate ion source-selected from the group consisting of sulfuric acid, an ionizable salt of sulfuric acid and sulfur dioxide and a (2) contacting said sulfate-containing molybdenum sour'cewith a mixture of hydrochloric acid and an oxygen-containing gas ata temperature of at least 1 250 C. to volatilize the molybdenumin a chloride form. .1.

2. An improved process for therecovery of molybdenum from sourcesthereof containing alkaline earth molybdates which comprises I (l) contacting said molybdenum source with an amount of a sulfate ion' source selected from the group consisting of, sulfuric acid, an ionizable salt of sulfuric acid and sulfur dioxide at least stoichiometrically equal to the molybdenum present therein, and p (2) contacting said sulfate-containing molybdenum source with a mixture of hydrochloric acid and air at a temperature of between about 250 C. and about 800 C. to volatilize the molybdenum values therefrom in a chloride form. p

3. The process of claim 2 wherein the sulfate is sulfuric acid.

4. The process of claim 2 wherein the sulfate is sodium sulfate. v

5. The process of claim 2 wherein the sulfate is derived from S0 and air.

6. The process of claim 2 wherein the temperature is from about 300 C. to about 600 C.

7. The processof claim 5 wherein the molybdenum source contains magnesium molybdate. I

8. The process of claim 5 wherein the molybdenum source contains calcium molybdate.

References Cited OSCAR R. VERTIZ, Primary Examiner. HERBERT T. CARTER, Examiner. 

